Method and system for quantifying hepatic fat in humans

ABSTRACT

A probe unit ( 100 ) including a magnet ( 102, 103 ) generates a static magnetic B 0  field in an examination region and a RF coil ( 105 ). An input-output module ( 201 ) includes a transmitter ( 203 ) which controls the RF coil ( 105 ) to excite resonance and cause echoes ( 210 ) and a receiver ( 204 ) which demodulates and digitizes the echoes ( 210 ). A data processing module ( 206 ) includes at least one processor programmed to calculate a T 2  relaxation distribution plot from a digitized echo ( 210 ) train, calculate a first area under the fat peak on the T 2  distribution plot, calculate a second area under a water peak on the T 2  distribution plot, and normalize the first and second area to determine a fat-to-water ratio.

The present application relates to monitoring of hepatic fat in asubject through nuclear magnetic resonance (NMR).

Recent medical resonance imaging (MRI) studies have focused onquantifying the amount of hepatic fat in patients. Hepatic fatquantification can be used to detect Non-alcohol Fatty Liver Disease(NAFLD) and to monitor the effect of treatment of the disease. NAFLDoccurs when an abnormal amount of fat is retained in the liver, theaccumulation known as steatosis, for reasons not related to excessivealcohol use. If patients are left untreated, they may developdegenerative liver disease, including fibrosis, cirrhosis, andhepatocellular carcinoma.

Currently, relevant clinical information for detecting and monitoringNAFLD has been provided by MRI and the generation of fat fraction mapsthrough the mDIXON method. Invasive biopsy procedures have also beenused to detect NAFLD and monitor treatment. The main drawbacksassociated with these methods are excessive cost, limited patientaccess, and invasiveness. At-risk patients (pre-diabetic, Type-IIdiabetics, obese patients, etc.) would benefit from a lower cost methodto test for hepatic fat that can be easily performed in outpatientclinics or physician offices.

The present application provides a new and improved monitoring systemwhich overcomes the above-referenced problems and others by offering alow-cost, non-invasive, and accessible solution. Similar to theapparatus employed in oil well logging systems, a portable magnet systemis proposed which detects the NMR properties of an outside environment(R. L. Kleinberg et al., Novel NMR Apparatus for Investigating anExternal Sample, Journal of Magnetic Resonance 97, 466-485 (1992)). Thissystem differs from the conventional NMR apparatus, wherein a sample isfit inside of a surrounding magnet and RF coil, by creating a staticmagnetic field along an external surface and investigating samplesoutside of a magnet and coil. This configuration is also known asinside-out NMR. A magnetic field of relatively low homogeneity is formedalong an external surface and a small RF coil is used to perform NMR ona patient's liver. Analysis of time relaxation constants similar to thatperformed in table-top food analyzers allows for the amount of hepaticfat to be easily quantified.

While the use of an NMR apparatus to investigate an external sample hasbeen substantively disclosed in the oil well logging industry, there isa need to create a low cost and accessible NMR system for detecting andmonitoring the level of hepatic fat in patients.

In accordance with one aspect, a magnetic resonance system forquantifying an amount of fat in a patient is provided. The systemincludes a probe unit with a magnet and RF coil and a data acquisitionapparatus with an input-output module and at least one processor. Themagnet generates a static magnetic B₀ field in an examination regionoutside of the probe unit. The input-output module receives a RFresonance signal from the RF coil and converts it to digital data. Theat least one processor analyzes the digital data signal in order todetermine the amount of fat in a patient.

In accordance with another aspect, a method for quantifying an amount offat in a patient is provided. The method includes positioning a probeunit adjacent to a region of interest to generate a static B₀ magneticfield, transmitting a RF excitation signal to the region of interestwith a RF coil included in the probe unit to excite resonance, receivingRF signals from the region of interest, converting the resonance signalsto digital MR data, and analyzing the digital MR data to calculate afat-to-water ratio.

In accordance with another aspect, an apparatus for quantifying theamount of hepatic fat in a patient is provided. The apparatus includes aportable NMR probe and at least one processor programmed to calculate aT₂ relaxation distribution plot from a digitized magnetic resonance echosignal, calculate a first area under a hepatic fat peak and a secondarea under a water peak located on the T₂ relaxation distribution plot,and normalize the first and second area to generate a hepaticfat-to-water ratio.

One advantage resides in providing a low-cost system for quantifyinghepatic fat.

Another advantage, particularly for at-risk patients, is that hepaticfat monitoring can be performed in outpatient clinics or physicianoffices.

Another advantage resides in visually depicting the quantity of hepaticfat and a fat-to-water ratio for a patient on a display.

Yet another advantage resides in quickly providing diagnosticinformation to a patient regarding their liver environment, such as thelikelihood of an overabundance of iron or degenerative liver diseases.

Still further advantages of the present invention will be appreciated tothose of ordinary skill in the art upon reading and understanding thefollowing detailed description.

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating the preferred embodiments and arenot to be construed as limiting the invention.

FIG. 1 is a schematic diagram and functional block diagram of a systemfor quantifying an amount of hepatic fat in a patient according to oneembodiment of the present application;

FIG. 2 is graph which illustrates a Carr-Purcell-Meiboom-Gill (CPMG)spin echo technique implemented by one embodiment of the system of FIG.1;

FIG. 3 is a graph which illustrates a T₂ relaxation distribution plotillustrating hepatic fat, bound water, and free water peaks;

FIG. 4 is a flow diagram of a method of quantifying the amount of fat ina patient according to another embodiment of the present application;

FIG. 5 is a flow diagram which illustrates the method in FIG. 4 inaccordance with another embodiment of the present application.

With reference to FIG. 1, a portable NMR probe 100 performs low-field,time domain nuclear magnetic resonance (TD-NMR) inside of target tissue,e.g. a liver, of a patient 300 in a region defined as the sensitive zone301. A static B₀ magnetic field is generated by two or more magnetpieces 102 and 103 of opposite polarity that are mounted in abiocompatible base or housing portion 101. This B₀ magnetic field alignsthe spin states of hydrogen nuclei found within the sensitize zone 301.A suitable material for magnets includes samarium cobalt, niobium, otherrare earth magnets, electromagnets, and the like. However, othermagnetic materials are contemplated as are known to those havingordinary skill of the art. The biocompatible base portion is preferablypositioned above the lower right lobe of a patient's liver. In oneembodiment, the magnets are configured such that within 5 cm of themagnet pieces 102 and 103, the static magnetic field lines extendtransversely with approximately 100 ppm homogeneity and the sensitivezone 301 is a few centimeters. This region of relative field homogeneityis where NMR data is most easily and accurately acquired.

The location of the region of magnetic homogeneity is controlled, in oneembodiment, by the geometry of the magnet pieces 102 and 103. Increasinga gap distance 110 between the magnet pieces 102 and 103 decreases thedepth of the homogenous field region in the sensitive zone 301, whilereducing the gap increases the depth. In another embodiment, anadditional magnet piece 104 is movably disposed between the two magnetpieces 102 and 103 to alter the depth of the homogenous field region. Byway of example, magnetic field lines of increasing depth in thesensitive zone are indicated as 107, 108, and 109.

The magnetic field can also be focused with the use of a passive oractive focus element 106 disposed between the magnets and the sensitivezone. This element can take on a variety of shapes and sizes, includinga fixed, telescoping, or adjustable annular ring. The focus element 106contracts to narrow the magnetic field and expands to broaden themagnetic field.

Handles or a piston grip for a handheld embodiment or mountingstructures for a robotically supported embodiment also extend from thebiocompatible base or housing 101 for positioning of the portable NMRprobe 100 to create the static B₀ magnetic field in the sensitive zone301, e.g. contacting the patient's skin over the liver region to beexamined.

The portable NMR probe 100 also includes an RF coil 105, which is placedin a cavity between the two magnet pieces 102 and 103. The RF coil 105can be of varying sizes and configurations. The RF coil 105 ispreferably made of a high-conductivity material that maximizes asignal-to-noise ratio. The RF coil 105 in one embodiment includes twocurrent opposed loops which produce an RF or B₁ field perpendicular to aface of the coil. The RF coil 105 in another embodiment is afigure-eight shaped coil. Other coil configurations include single loopcoils, coil arrays, focused coils, directional coils, quadrature coils,the like are also contemplated. Separate transmit and receive coils ofdifferent configurations are also contemplated.

The RF frequency of the RF coil 105 is adjustable to the Larmorfrequency at the B₀ field strength of selectable depths such as 107,108, and 109. With continuing reference to FIG. 1 and further referenceto FIG. 2, a transmitter 203 of an input output module controls the RFcoil 105 to generate an RF excitation pulse 208, e.g. a 90° pulse, atthe Larmor frequency, to form an excitation field or pulse perpendicularto the B₀ static magnetic field. The Larmor frequency (ƒ_(L)) in thisapplication is defined as ƒ_(L)=λ_(H)B₀, where λ_(H) is a gyromagneticratio for hydrogen (42.57 Mhz/T) and B₀ the strength of the static B₀magnetic field. Because the gyromagnetic ratio of hydrogen varies withhow the hydrogen is bound to other atoms, the RF frequency is typicallya spectrum that spans resonance frequencies of the target tissues. ThisRF excitation pulse 208 excites (tips) the hydrogen nuclei within thesensitive region 301 and causes them to precess around the axis of theB₀ magnetic field with the Larmor frequency. The transmitter 203 alsocontrols the RF coil 105 to generate 180° inversion pulses 209 toreverse the precession and cause magnetic resonance echoes. The RF coil105 also receives resonance RF signals, particularly echoes 210 from thenuclei excited to resonance.

Over time, the resonance signal looses energy as the magnetizationprecesses back into alignment with the B₀ field at a rate 211 which isproportional to 1/T₂ relaxation time. Since the T₂ relaxation timesdiffer for the hydrogen in fats, bound water, free water and otherchemical bonding states, NMR can differentiate between molecules such aslipids and water. Lipids have a greater electron density than water andthe resonance signal from lipids decays faster than the resonance signalfrom water, i.e. the T₂ of lipids is shorter than the T₂ of water.

The input-output module 201 includes a transmit/receive switch 202, thetransmitter 203, and a receiver 204. The transmit/receive switch 202connects either one of the transmitter or the receiver to the RF coil105. The transmitter 203 is typical of those found in modern MRIdevices, including the ability to modulate a digital signal input to anoutput RF signal. The receiver 204 is also typical of those found inmodern MRI devices, including the ability to demodulate, amplify, anddigitize a received RF resonance echo signal. The transmitter 203 isconnected to a controller 205 which controls the transmitter 203 totransmit a selected magnetic resonance sequence at a frequency thatexcites and manipulates resonance in the magnetic field at a selecteddepth. For example, the controller causes the transmitter 203 totransmit a Carr-Purcell-Meiboom-Gill (CPMG) sequence to excite resonanceand manipulate the resonance to create the series of echoes 210. Asillustrated in FIG. 2, the CPMG sequence includes a excitation pulse208, such as a 90° pulse, to excite resonance and a series of 180°inversion pulses 209 to repeatedly refocus the magnetization into theseries of echoes 210.

With particular reference to FIG. 2, the RF excitation pulse 208transmitted from the RF coil 105 excites an exponentially decayingresonance signal 211. As the resonance signal decays, hydrogen nucleireturn to their equilibrium state through various relaxation processes.Their precession frequency is dependent upon the local magnetic fieldstrength B₀. Due to the different resonance (Larmor) frequencies of thehydrogen in different chemical bonding states, homogeneity variations inthe static B₀ magnetic field, and the like, hydrogen nucleimagnetization dephases over time as it decays. The inversion pulses 209flip the magnetization 180° causing the magnetization vector componentsof the various resonance frequencies to start rephasing. Although theCPMG pulse sequence is illustrated, other sequences, such as Pulse FieldGradient Spin-Echo (PFGSE), Carr-Purcell (CP), or the like are alsocontemplated.

The multi-exponential rate of decay 211 of spin-echo peaks 210 ischaracterized by the T₂ relaxation time, also known as the spin-spinrelaxation time. The decaying resonance signal includes a train of thespin-echo peaks 210 which occur between phase recovery inversion pulses209. The series of echoes 210 generated by the CPMG sequence getprogressively smaller as the excited resonance decays.

A data acquisition unit 200 is built into or connected to the portableNMR probe 100. The data acquisition unit 200 is controlled by thecontroller 205 to apply pulse sequence radiofrequencies to a patient300, perform data acquisition, and process data to generate qualitativemeasurements of fat and water in the sensitive zone 301. A dataprocessing unit 206 receives the echo signals 212 from the receiver 204.Because the H¹ dipole in free water, bound water (e.g. liver tissue),and lipid (e.g. hepatic fat) resonates at characteristically differentbut close frequencies, each signal is a composite of free water, boundwater, and lipid signals. Each signal measured can be represented by asum of exponentials, as shown in Eqn. 1 below, in which the overallmulti-exponential rate of decay 211 contains contributions from thedecay of free water, bound water, and lipid.

S(t)=Σ₀ ^(T2 max) Aexp(−t/T2)  (1)

S is the signal measured by the receiver 203 at time t, which isproportional to the total number of H¹ dipoles resonating at time t. Arepresents amplitude of the signal. The summation is performed from T₂=0ms to T₂ max, which is the longest value of T₂ on the end of the CPMGsequence. There will be separate terms in equation (1) for free water,bound water, and lipid. Referring to FIG. 2, signal readings at a numberof time points corresponding the spin echo peaks 210 (e.g. 2t, 4t, 6t,8t) are used to solve equation (1) for T₂.

An analyzer unit or module 207 uses a fitting technique to calculate theinversion of multi-exponential equation (1) and determine a T₂relaxation distribution, which is represented graphically in FIG. 3. Forexample, the analyzer unit 207 applies a transform to the string ofechoes 210 from the frequency domain, e.g. a Fourier Transform. Fittingtechniques include smoothing methods, singular value decompositions(SVD), solid iteration rebuild techniques (SIRT), and those othermethods commonly employed to solve a linear inversion problem. Theanalyzer plots a T₂ relaxation distribution graph similar to that seenin FIG. 3, which shows a separation of the signal from the spin echoes210 into a free water peak 210 a, bound water peak 210 b, and a lipidpeak 210 c.

With containing reference to FIG. 3, the lipid T₂ peak 210 c has ashorter T₂ relaxation time relative to water due to the increasedelectron density around hydrogen nuclei in lipids compared to water.Bound water has an increased electron density relative to free water,and therefore has a longer T₂ than lipid and shorter T₂ than pure water.Bound water and free water may occur in partially overlapping peaks.

A normalizing unit 212 calculates the area under the lipid peak anddivides it by the area under the corresponding water peaks to generate anormalized lipid value, e.g. percent lipid. In a healthy liver region,the lipid (hepatic fat) value will be very small. The lipid value isdisplayed on a display device 216, e.g. a video monitor, printer, or thelike and/or saved to memory. A diagnostician uses this lipid value todiagnose fatty liver diseases.

The echoes contain other diagnostic information. As previouslymentioned, the T₂ relaxation time is inversely proportional to a rate ofdecay of the peaks of the echoes 210. A T₂ calculating unit 213calculates a mean T₂ relaxation time value for the water peaks,particularly the bound water peaks. The mean T₂ relaxation times arerepresented by the peak value of free water peak 210 a, bound water peak210 b, and lipid peak 210 c in the T₂ relaxation time distribution plot.The more iron (Fe) in the liver tissue, the faster the rate of decay andthe shorter T₂ of the bound water. A conversion unit or module 214, suchas a look up table, converts the calculated mean T₂ relaxation time intoa level of iron which is displayed on a display unit 216 and/or saved tomemory.

The T₂ relaxation time is also indicative of other properties of theliver or other anatomical regions. Trapped fluids increase the T₂relaxation time. The T₂ calculating unit 212 calculates the mean T₂relaxation time and the conversion unit 214 converts it to meaningfulvalues indicative of the amount of trapped fluid for display on thedisplay 216 and/or saving to memory.

Other changes in the liver structure also change the T₂ relaxation time.For example, fibrosis, cirrhosis, and other conditions which stiffen theliver, shorten the T₂ relaxation time for both water and lipid. The T₂calculation unit 212 calculates the T₂ relaxation times for both thewater and lipid peaks and the conversion unit 214 converts the T₂relaxation times for appropriate stiffness units for display and/orstoring.

In one embodiment, a computer analysis system such as a common computerbased diagnosis recommendation system analyzes the T₂ relaxation timesof various components in the body along with other available informationto generate a proposed diagnosis which is displayed on the display unit216.

In another embodiment, the analyzer unit or module 207 separates thereceived echo peak signal into a free water peak, bound water peak, anda lipid peak in the frequency domain by applying a Fourier Transform.The analyzer unit 207 includes fast Fourier transform (FFT) algorithms,discrete Fourier transform (DFT) algorithms, or the like. A frequencyspectrum plot is generated similar to those of NMR spectrometers, inwhich hepatic fat peaks have a lower resonance frequency relative tofree water and bound water. The area under the lipid peaks is divided bythe area under the water peaks to normalize the data. Standard frequencyspectrum plots representative of different conditions of the liver orother anatomical regions are located in the conversion unit 214, whichcompares measured frequency spectrum plots with the standard frequencyspectrum plots to generate a value indicative of clinical informationrelated to the condition(s). This value is displayed on a display unitand/or saved to memory.

In another embodiment, the data-acquisition device 206 interacts with atleast an auxiliary magnet to increase the strength of the B₀ staticmagnetic field within the sensitive zone 301 and increase resolution ofthe frequency spectrum plot. This auxiliary magnet includes a roboticswing arm magnet, cancelling magnets or other the like. The auxiliarymagnet would is positioned in such a way as to decrease leakage of themagnetic field generated in the sensitive zone 301.

The entire system indicated in FIG. 1. is expected to cost approximately$30,000 (

20,000) with approximate dimensions of no larger than 10×40 cm. Even fatfraction determinations that have an absolute error of <10% stillprovide relevant clinical value. In addition, by virtue of the low fieldand the sampling method used, no room RF shielding should be necessary,making the installation of the system relatively simple within aphysician's office or outpatient clinic.

The above described units and modules may include individual units suchas application-specific integrated circuits (ASICs) or processors,program routines of one or more processors programmed to perform theabove and below discussed steps, or the like.

In another embodiment, the output of the analyzer unit 207 is sent tothe conversion unit 214, which includes a lookup table. The lookup tableincludes constants for lipid and water, including molecular size andweight. The lookup table also includes verified experimental dataindicating how T₂ values shift in the presence of an overabundance ofiron, cystic lesions, or degenerate liver diseases such as fibrosis,cirrhosis, and heptacellular carcinoma. The conversion unit 214 comparesthe calculated data output from the analyzer 207 in order to formulatediagnostic information. A report generator 214 decides which informationto output and a display format for the display unit 216, e.g. a videomonitor, printer, or the like and/or saved to memory. This informationis preferably a diagnostic report which indicates the likelihood ofliver abnormalities. The diagnostic report indicates at least hepaticfat fraction information for review by a physician or other operator.

With reference to FIG. 4, a method for quantifying an amount of fat in asubject begins at a step S402, in which the NMR probe 100 is positionedsuch that its static B₀ magnetic field is established in a region ofinterest 301. This region of interest 301, in the hepatic fatembodiment, includes a few cm region of magnetic field homogeneity thatis ideally located in the lower right lobe of the liver. The homogenousmagnetic field region is located at a selected depth within the regionof interest based on probe position or adjusting magnetic fieldgeometry, magnetic field focus, or the like. Generation of a uniformstatic B₀ magnetic field causes the spin-states of hydrogen dipoleswithin the region of interest to preferentially align in either aparallel or anti-parallel orientation. However, B₀ fields with knowninhomogeneities are also contemplated.

At S403, a modulated RF signal is transmitted to the region of interest301 to form a B₁ excitation field. The modulated signal originates as adigital signal sent by the transmitter 203 under control of the dataprocessing unit 206 to the RF coil 105 for transmission to theexamination region. A B₁ excitation field pulse 208 causes hydrogennuclei to precess around the B₀ field at the Larmor frequency. At S405,a 180° B₁ field inversion pulse 209 is applied to reverse the precessionand causes the magnetic resonance echo 210. In the CPMG sequence, the180° pulses are applied periodically to generate the series of echoes210 illustrated in FIG. 4. At S406, the induced magnetic resonancesignal is picked up by the coil 105 and converted to digital MR data bythe receiver 204.

At S407, the digital MR data is sent to the analyzer 207 from thereceiver 204 and analyzed to produce a T₂ relaxation distribution plot.The analysis includes inversion of the summation of a multi-exponentialdecay 211, the summation shown in equation (1), which can be performedby common algorithms for solving an inversion problem. The T₂ relaxationtime distribution plots amplitude against T₂ relaxation time similar toFIG. 3. Separation of a free water peak 210 a, bound water peak 210 b,and lipid peak 210 c is noticeable from the plot.

At S412, an area under the respective peaks of the T₂ relaxationdistribution plot is normalized to produce a fat-to-water ratio. Tocalculate the fat-to-water ratio, the normalizing unit 212 calculatesthe area under the lipid peak and divides it by the area under thecorresponding water peaks to generate a normalized lipid value, e.g. afat-to-water ratio or percent lipid.

With reference to FIG. 5, another embodiment of a method of quantifyingthe amount of fat in a patient is contemplated. At step S407 a T₂relaxation distribution plot is generated based on analysis of digitalMR data. At S412, the area under the T₂ relaxation distribution plot isnormalized to calculate a fat-to-water ratio. At S413, a mean T₂relaxation time is calculated for each of the constituent peaks in theT₂ relaxation distribution plot. At S414A, the calculated fat-to-waterratio is correlated with pre-determined information on the conversionunit 214, such as a lookup table, to generate diagnostic informationabout a patient. The pre-determined information can include commonfat-to-water ratios for different anatomical conditions. Informationrelevant for the region of interest being examined would be used by theconversion unit 214 to generate diagnostic information.

At S414B, the calculated mean T₂ relaxation time from S413 is correlatedwith pre-determined information stored on the conversion unit 214, suchas a lookup table, to generate diagnostic information. The conversionunit 214 includes verified experimental data predicting upward anddownward shifts in T₂ corresponding to different environmentalconditions of the liver. By means of example, a substantial decrease inT₂ for bound water indicates an abundance of iron in the liver. A slightdecrease in T₂ for bound water, which is a noticeably smaller decreasethan realized for an overabundance of iron, would indicate degenerativeliver disease such as fibrosis, cirrhosis, and heptacellular carcinoma.

At S415, a diagnostic report is generated which includes a variety ofdiagnostic information, such as a calculated fat-to-water ratio or otherdiagnostic information. The diagnostic report may include just afat-to-water ratio, or the diagnostic information generated at S414Aand/or S414B. With a comprehensive lookup table, the diagnosis ofparticular anatomical conditions would become increasing accurate asmore diagnostic readings are taken. In one embodiment, a diagnosticreport generated by the report generator 215 is displayed on a display216, e.g. a monitor or printer. The diagnostic report includes thepercent likelihood of different liver conditions based on T₂ changes. Toincrease accuracy of the diagnosis, information derived from theshifting of calculated mean T₂ values may be combined with informationderived from calculated fat-to-water ratios.

At S416, the diagnostic report generated at S415 is viewed by aphysician or operator to recommend further treatment for a subject andstored in a medical records database.

It should also be appreciated that while water and lipid generally havesomewhat similar T₂ relaxation constants, the difference is morepronounced in the liver. This increases the diagnostic value of thepresent application of TD-NMR in the liver. A normal amount of iron inthe liver environment has also been shown to not affect results.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. A magnetic resonance system for quantifying an amount of fat in apatient, comprising: a portable probe unit positionable adjacent thepatient, the probe unit including: a magnet which generates a staticmagnetic B₀ field in an examination region outside of the probe unit;and an RF coil disposed in the probe unit adjacent to a region ofinterest; a data acquisition apparatus connected to the RF coil, thedata acquisition apparatus including: an input-output module whichreceives a RF resonance signal from the RF coil and converts it to adigital signal; and at least one processor which analyzes the digitalsignal from the input-output unit to determine the amount of fat in thepatient.
 2. The system according to claim 1, wherein the region ofinterest is a right lobe of a liver.
 3. The system according to claim 1,wherein the at least one processor is programmed to perform the stepsof: analyzing digital MR data to generate a T₂ relaxation distributionplot; calculating a mean T₂ relaxation time for at least one peak of theT₂ relaxation distribution plot; converting a calculated fat-to-waterratio and a calculated mean T₂ relaxation time into diagnosticinformation.
 4. The system according to claim 3, wherein the at leastone processor is further programmed to perform at least one of:normalizing an area under the T₂ relaxation distribution plot tocalculate a fat-to-water ratio; determining whether a patient has anoverabundance of iron; and determining whether a patient has ananatomical disease.
 5. The system according to claim 1, wherein the atleast one processor is further programmed to: transmitting a RF signalto the region of interest to form a B1 excitation field; applying a 180°inversion pulse to generate a magnetic resonance echo; receiving aresonant RF signal from the echo and converting it to digital data;analyzing digital MR data to generate a T₂ relaxation distribution plot.6. The system according to claim 1, wherein the at least one processorsends a digital signal to the input-output module to move the staticmagnetic B₀ field.
 7. The system according of claim 1, wherein the atleast one processor includes: an analyzer; a T2 calculator unit; and anormalizing unit.
 8. (canceled)
 9. (canceled)
 10. A method forquantifying an amount of fat in a patient, comprising: positioning aportable probe unit adjacent a region of interest to generate a staticB₀ magnetic field in the region of interest; transmitting an RFexcitation signal to the region of interest with an RF coil disposedbetween the probe unit to excite resonance; receiving RF resonancesignals from the region of interest; converting the resonance signals todigital MR data; and analyzing the digital MR data to calculate afat-to-water ratio.
 11. The method according to claim 10, wherein theregion of interest is a right lobe of the liver.
 12. The methodaccording to claim 10, further including: analyzing digital MR data togenerate a T₂ relaxation distribution plot; calculating a mean T₂relaxation time for at least one peak of the T₂ relaxation distributionplot; and converting a calculated fat-to-water ratio and a calculated T₂relaxation time into diagnostic information.
 13. The method according toclaim 10, further including at least one of: normalizing an area underthe T₂ relaxation distribution plot to calculate a fat-to-water ratio;determining whether a patient has an overabundance of iron; determiningwhether a patient has an anatomical disease.
 14. The method according toclaim 10, further including after exciting resonance applying a series180° inversion pulses to generate a magnetic resonance echoes which areanalyzed to calculate the fat-to-water.
 15. The method of claim 10,further including: transforming digital data through Fourier transformto generate a T₂ relaxation distribution plot; and normalizing an areaunder the T₂ relaxation distribution plot to calculate the fat-to-waterratio.
 16. (canceled)
 17. (canceled)
 18. The system according to claim10, further including adjusting the region of interest by moving thestatic B₀ magnetic field further from and closer to the probe unit. 19.A non-transitory computer readable memory which carries computer codewhich controls one or more processors to perform the method according toclaim
 10. 20. An apparatus for quantifying the amount of hepatic fat ina subject, comprising: a portable NMR probe which generates a staticmagnetic B₀ field in a region of interest; at least one processorprogrammed to: calculate a T₂ relaxation distribution plot from adigitized magnetic resonance echo signal; calculate a first area under ahepatic fat peak located on the T₂ relaxation distribution plot;calculate a second area under a water peak located on the T2 relaxationdistribution plot; and normalize the first and second area to generate ahepatic fat-to-water ratio.